147 - Quantitative pO2 Mapping Using Electron Paramagnetic Resonance Imaging in Orthotopic Murine Glioma

Abstract

Glioblastoma is the most frequent primary malignant brain tumor and its malignant nature is closely associated with hypoxia. Thus, it would be useful for treatment of glioblastomas to evaluate intratumoral distribution of hypoxia for determining the therapeutic planning as well as assessment of its effectiveness during the therapy. Electron paramagnetic resonance imaging (EPRI), is an imaging technique which can generate quantitative maps of oxygen in vivo using the exogenous paramagnetic compound, triarylmethyl. In this study, we examined the feasibility of EPRI for assessment of oxygen distribution in the orthotopic glioblastoma models of U251 and U87. Heterogeneous distribution of pO2 between 0 and 50 mmHg was observed throughout the tumors except for the normal brain tissue. U251 glioblastoma was more likely to be exposed to hypoxia than U87 (median pO2; 29.7 mmHg and 18.2 mmHg, P = 0.028, in U87 and U251, respectively). The ratio of hypoxic fraction where pO2 was less than 10 mmHg showed a good correlation with pimonidazole-positive region. In subcutaneous xenograft model, irradiation was relatively less effective for U251 compared to U87, suggesting the high population of hypoxic cells. In conclusion, EPRI is a feasible method to evaluate oxygen distribution in the brain tumor.